That's not to say that the PSD can't have the "destroy the threat" component, just that he can function adequately as a PSD without it. Perhaps the extra edge may make him a liability used for apprehension, too much injury inflicted on the suspect. I don't know that for a fact, maybe a very experienced PSD handler can answer this.
I suppose a PD can function to a degree without the "in it for the fight" component, but for my purposes that's not an ideal mindset for the dog.
If you don't understand what I mean by "in it for the fight", the dog enjoys the fight and is happy to continue. He can withstand a lot of pressure. But the handler is always there to end the fight. It is in essence a very rough game. The dog will only switch his bite to keep the game going, if the bite is giving him too a hard time, or not enough of a good time.
A dog that wants to end the fight will bite to hurt and incapacitate his opponent. There are not a lot of dogs that can learn this working on a suit. The dog actually has to be strong enough to somewhat hurt the man through the suit for this to happen. I don't know that there's a decoy skilled enough to offer the necessary reaction if he's not really feeling anything, the timing has to be perfect.